A conventional cage implant is described, for example, in patent application FR2861582. Its external profile is curved in a bean-shaped and is designed to be inserted between two vertebrae using the posterior transforaminal approach. In other words, the axis of the implant, according to which it is inserted into the disc space, is curved. The implant has an interior cavity designed to contain either a natural or synthetic bone graft material, which is why the implant is referred to as a “cage.” The cage is open at both the upper and lower ends to allow the bone graft to come into contact with the respective vertebral bodies in order to achieve a definitive fusion between the vertebral bodies.
Intersomatic arthrodesis is performed using a posterolateral approach following resection of all or part of the posterior facet joints, through an interstice between the dural sheath and underlying root. Once inserted, the implant moves to the anterior part of the disc space by rotating 90° between the vertebral bodies to reach its final position, expanding transversally in the disc space.
The implant is pre-filled with a bone graft material prior to insertion. That is because, once placed in its final position, the implant is no longer accessible.
The insertion of that type of implant into often highly-pinched discs requires placement of pedicular screws beforehand to open up the disc space. Furthermore, another complicating factor is the difficulty of turning the implant 90° in such a restricted space while rotating it at the same time because the screws only open the posterior part of the disc space.
Expandable implants have been proposed to allow for more effective opening of the disc space than with a pedicular screw. For example, U.S. Patent Application Serial No. 2006/0129244 describes an expanding device designed to be inserted between two vertebral bodies that is composed of two plates and an expanding part that slides between the two plates along the axis of the implant in order to separate the two plates between an unexpanded position and an expanded position.
That type of device will provide for better opening of the disc space. However, it is still very difficult or even impossible to insert bone graft material using such a device, particularly into the anterior part of the implant.
Accordingly, it is an object of this invention to provide an implant that can be inserted using an anterior transforaminal approach between two adjacent vertebrae, and allows for easy insertion of bone graft material.